1. Field of the Invention
The present invention relates to an improved tibial tray that is positioned on the patient's tibia for joint replacement in a total knee arthroplasty. The improved tibial tray of this invention is of a unitary construction and comprises a unique, asymmetric keel that permits insertion through a relatively smaller incision.
2. Description of the Prior Art
Total knee arthroplasty is a common procedure performed worldwide. This procedure traditionally requires wide exposure of the distal femur and proximal tibia in order to permit appropriate preparation of the bone surfaces for implanting the components. Most implants performed today in the United States are cemented in place with polymethylmethacrylate cement. Extraneous cement is traditionally cleaned, requiring additional exposure of the femur and tibia to ensure sufficient removal and to prevent potential third body debris.
Over the past several years there has been a movement toward less invasive techniques for total knee arthroplasty. These less invasive techniques typically involve smaller incisions, less disruption of the musculature of the knee, and decreased visualization when compared to that of “traditional” total knee arthroplasty. One of the major technical hurdles in performing an accurate, minimally invasive total knee arthroplasty is obtaining adequate exposure in order to seat the currently available components, particularly the state-of-the-art tibial trays.
Traditionally, the tibial tray is cemented in place and has a relatively large keel, or a depending stem, used to control angular and rotational forces that are imparted to the tibial tray by the knee joint. Because of the size of such keels or stems today, the proximal tibia must be circumferentially exposed in order to allow appropriate preparation of the bone and seating of the implant. This requires subluxation of the tibia anteriorly and clearance of the posterior lateral femoral condyle to prevent iatrogenic fracture or improper seating of the components.
Furthermore, as the tibial tray is cemented in place, the most common method of prosthetic fixation, additional exposure is also necessary to debride cement as it extrudes from under the tray as the tray is forced into position. Even when traditional large incisions are used, the procedure is challenging. With the advent of minimally invasive techniques, another level of difficulty is added because the components must be placed through smaller incisions in the patient's skin.
One means for solving the problem is shown in prior patented devices as modular tibial trays. By use of the term “modular” it is meant that the trays include a keel or stem that is separate from the tibial base plate. In order to facilitate minimally invasive insertion, the keel or stem is inserted into the tibia, and the base plate is attached thereto. However, a relatively larger incision is still necessary for insertion of the keel or stem, and modular devices are frequently more expensive than unitary devices, and the parts may not mate properly. Furthermore, intraoperative assembly is necessary, and this may prove to be more difficult when working through small incisions. Finally, modularity can result in modular interface fatigue fracture, fretting, and/or debris generation that can compromise the effective life of the arthroplasty.